Annual operating hours in Lahti Energy Ltd’s coal fired power plant have been decreased. Reason for the decline is the commissioning of the new gasification power plant in 2012. Since then there has not been demand for coal fired power plant during summer months. During the power plant’s downtime, steam power process ought to be preserved. The preservation refers to measures in keeping the devices corrosion free. The presence of either moisture or oxygen will be prevented depending on the method of preservation. This thesis examines various methods of preservation, aiming to find the best solution for the steam power process. The work focuses on three methods to preserve the boiler. Nitrogen blanketing and wet preservation prevent the presence of oxygen and dry air preservation prevents the presence of moisture. Effects of the preservation methods to other equipment and systems are also studied. Based on the outcome of this study, it can be concluded that the most workable solution for the power plant’s last years in use is the dry air preservation. In case the power plant will be used as a reserve power plant, nitrogen blanketing is the most cost effective solution.